The conventional semiconductor switches manufactured by using micro-machining technology are operated on the principle that a high DC voltage is applied to thin dielectric films of SiO2, Si3O4 etc., to generate electrostatic force, which causes a cantilever or contact pad as the contact means, serving as the signal path, to repeatedly switch-on or -off the signal transmitting line.
FIG. 1 shows an example of semiconductor switch based on a conventional micro-machining technology using a cantilever in pull-down form. FIG. 1(a) shows a micro-machined switch in parallel form and FIG. 1(b) shows a micro-machined switch in serial form. As appreciated from the figures, the signal transmitting line 11 and the pad 13 for application of DC voltage to move a cantilever 12 are formed separately from each other in FIG. 1(a), while the signal transmitting line and the pad 14 for application of DC voltage are disposed on the same line in FIG. 1(b).
Such conventional micro-machined switches in pull-down form based on conventional art have a high isolation characteristic between short-circuiting and circuit-opening, with little signal loss, so as to be applicable in a wide frequency range from the microwave band to a band of extremely high-frequency waves corresponding to over 30 GHz.
The conventional micro-machined switch in pull-down form, as shown in FIGS. 1(a) and 1(b), is so formed that a DC voltage, capable of causing the generation of the electrostatic force strong enough to exceed the elastic force of the metal constituting the cantilever, is applied to contact the signal transmitting lines with the cantiliver and the returning of the cantilever for disconnecting circuit is conducted by the elastic force of metal.
For the semiconductor switch developed by using conventional technology, application of a DC voltage over 20 V was required to attract the metal constituting the cantilever so as to bring the cantilever into contact with the line for transmitting signals, so that there was a problem of needing a separate circuit for raising the electric voltage for driving communication system for the purpose of application to the communication system.
In addition, there is another problem of the short using life due to the material deformation of cantilever and the low reliability on the ground that the isolation of the signal transmitting line relies on the elastic restoring force of the cantilever forming metal.